The present invention is directed to a method of using a disposable reagent pack usable with analytical instruments and, in particular, to a method of using a reagent pack having an isolation well to control the length of exposure of a first fluid to a second fluid. Embodiments of the present invention control the length of exposure of the first fluid to the second fluid by allowing selective transfer of fluid between the wells containing the respective fluids.
In general, particle analyzers move suspended biological or industrial particles from a sample vessel to a sensor with a liquid system. The sensor detects, counts and identifies the particles in the sample solution. The liquid flow system then moves the sample into a waste container. Many of these analyzers need prepared samples for analysis. The preparation may involve mixing the sample with a reagent. A significant drawback of conventional blood cell analytic systems is their incapacity for simultaneous preparation and presentation to the analyzing equipment of both a red cell analytic sample and a white cell analytic sample. Typically, the collected blood is added to a reagent pack which conventionally is in the form of a single tube or container to which the reagent fluid is added for either a red blood cell count or a white blood cell count. This requires the preparation of two separate analytic samples and the performance of two complete analytical machine cycles. Very often the reagent pack is made of glass which adds handling and disposal problems.
In addition, the current design of most reagent packs requires the direct application of a blood sample to a lysing reagent used in performing a white blood cell analysis. The length of time between exposing the blood sample to the lysing reagent and the performance of white cell differentiation or counting, for example, may vary from one sample to another and from one lab to another. It has been determined that the length of exposure of a blood sample to a lysing reagent of the cationic detergent family, i.e. quaternary ammonium salts, results in cell impedance changes. Therefore, because of this variation in the length of exposure, it is difficult to obtain results which are easily reproducible from one test to another, from one lab to another or even one lab technician to another. U.S. Pat. No. 4,485,175 (Ledis et al.) discloses altering the kinetics of the reaction in an automated instrument to solve this problem, for example, by predilution of the sample or slow addition of the sample to the reagent.
It is desirable to provide a disposable reagent pack wherein the length of exposure time of a first fluid, such as a blood sample, to a second fluid, such as a lysing reagent, is controllable, accurate and reproducible. In addition, it is desirable to provide a disposable reagent pack that is lightweight and durable and which enhances an analytical instrument's efficiency by simultaneously providing both a prepared red blood cell sample and a prepared white blood cell sample for analysis.